This proposal takes an integrative approach to metabolic regulation at the level of the intact organism, where the differentiaied cells which sense hypoglycemia will be characterized in normal and diabetic animals. The metabolic system in mammals is organized to guarantee an adequate supply of fuel to the central nervous system. When the blood sugar is low enough that central metabolism begins to diminish, an orchestrated hormonal response occurs which increases endogenous glucose production, and which diminishes glucose utilization by non-essential tissues. There is good evidence that the physiological mechanisms responsible for protection from hypoglycemia are deranged in the diabetic individual. Vital to the integrated hormonal response to hypoglycemia are the putative central nervous system glucoreceptors (PCGs) which sense the blood glucose level. In this proposal we will identify the location of, and examine the characteristics of the PCGs. To do this, we will exploit the "brain clamp" preparation, which was developed in our laboratory. This methodology, used in conscious animals, allows the control of local blood glucose concentration in selected regions of the CNS or other tissues of the body, independent of the systemic glucose concentration. By this approach, it is possible to examine the essentiality and characteristics of putative individual glucoreceptive tissues such as the hypothalamus, the hindbrain, or the hepato-portal circulation. It is planned to locate the site(s) of the most significant glucoreceptive regions, and examine their sensitivity to substrate supply and hormonal milieu under conditions of hypoglycemia induced by insulin, phlorizin, and/or somatostatin. These characteristics will also be examined in the diabetic animal, to elucidate the role of chronic insulin supply on glucoreceptor function.